Yes, you can use 20 watts or 30 watts.
No matter how high the wattage of the mobile phone charger you use, it can only charge according to the highest wattage of your mobile phone can accept.
If the phone supports fast charging, it must also be the charger that corresponds to the fast charging protocol to be able to fast charge.
This power is common to all mobile phones. 10w is equivalent to 5V2A, this current intensity is very low, will not do any harm to the phone. When we choose the charger, the power of the charger can not exceed the maximum power supported by the phone, otherwise it is easy to damage the phone. However, less than the charging power of the mobile phone does not matter, at most, the charging time is extended.